The present invention relates to a pneumatic fastener driving tool having an air exhaust arrangement, and more particularly, to the exhaust arrangement capable of weakening exhaust stream and reducing exhaust sound.
A pneumatic fastener driving tool urges an internal drive piston downwardly through a drive source such as a compressed air for driving a nail etc. into a wall or other intended location. The drive piston is reciprocally movable, and therefore, the compressed air applied to an upper portion of the drive piston must be discharged to an atmosphere during return stroke of the piston. To this effect, an exhaust port is formed at an upper portion of the driving tool for allowing the compressed air to be discharged outside. Due to the high pressure and rapid flow of the compressed exhaust air passing through the exhaust port, ambient dust or debris may be blown up by the compressed exhaust air stream, and further, loud or noisy exhaust sound may occur.
U.S. Pat. No. 5,110,030 discloses a cap formed with an exhaust port. The cap is rotatable with respect to an upper end portion of a main body in which the drive piston is reciprocally disposed. By manual rotation of the cap, angular position of the exhaust port can be changed, so that the exhaust air can be directed toward an intended direction for avoiding blowing-up of the dust or debris.
Further, in order to weaken the exhaust stream and to reduce the exhaust noise, a muffler member formed of an open cell type porous material is provided at the exhaust port as disclosed in a Japanese Utility Model application Kokai Nos. Sho-59-97882 and Sho-59-105379.
However, if the compressed air is frequently discharged due to the increased frequency of nail driving operation, adiabatic expansion occurs when the compressed air is discharged through the exhaust port to cool the exhaust port and the muffler member, which causes freezing of the muffler member. By this freezing, clogging occurs at the muffler, to prevent the exhaust air from passing therethrough. Thus, the fastener driving tool does not work.